Topological surface phonons modulate thermal transport in semiconductor thin films

TL;DR

This study reveals that low-frequency topological surface phonons, arising from acoustic nodal lines with a Berry phase of $2\pi$, meaningfully affect in-plane thermal transport in semiconductor thin films. By integrating first-principles-informed neural network potentials with the phonon Boltzmann transport equation and molecular dynamics, the authors quantify the surface-state contributions in Si, 4H-SiC, and c-BN for films under $<10\mathrm{nm}$ thickness, finding up to $\sim$30% contributions at room temperature and absolute contributions up to $82\,\mathrm{W\,m^{-1}\,K^{-1}}$. They develop a robust framework to distinguish surface- from bulk-dominated phonons and demonstrate that surface reconstructions and strain/temperature tune the transport, offering a route to topology-enabled thermal management in nanoscale devices. These findings provide the first quantitative assessment of topology-enabled phonon transport in semiconductors and highlight the significant role of topological surface phonons in nanoscale heat conduction.

Abstract

While phonon topology in crystalline solids has been extensively studied, its influence on thermal transport-especially in nanostructures-remains elusive. Here, by combining first-principles-based machine learning potentials with the phonon Boltzmann transport equation and molecular dynamics simulations, we systematically investigate the role of topological surface phonons in the in-plane thermal transport of semiconductor thin films (Si, 4H -SiC, and c-BN). These topological surface phonons, originating from nontrivial acoustic phonon nodal lines, not only serve as key scattering channels for dominant acoustic phonons but also contribute substantially to the overall thermal conductivity. Remarkably, for these thin semiconductor films below 10 nm this contribution can be as large as over 30% of the in-plane thermal conductivity at 300 K, and the largest absolute contribution can reach 82 W/m-K, highlighting their significant role in nanoscale thermal transport in semiconductors. Furthermore, we demonstrate that both temperature and biaxial strain provide effective means to modulate this contribution. Our work establishes a direct link between topological surface phonons and nanoscale thermal transport, offering the first quantitative assessment of their role and paving the way for topology-enabled thermal management in semiconductors.

Figures (6)

• Figure 1: (a) Schematic of the acoustic phonon nodal line (left) and the corresponding low-frequency topological surface states (right); (b) Sketch of three-phonon scattering processes in a thin film, and both bulk and topological surface phonons can participate in phonon scattering. Phonon dispersion relations of bulk (c) Si, (e) 4c-BN, and (h) 4H-SiC from first-principles calculations with their crystal structures. The Brillouin zones of bulk Si and c-BN, and 4H-SiC are shown in (d) and (g), respectively.
• Figure 2: (a)Schematic of the process using MLPs to predict topological surface phonons (Topo. SPs). Comparison of energies and atomic forces of (b, e) Si, (c, f) 4H-SiC, and (d, g) c-BN calculated from the DFT and NEPs for the training sets.
• Figure 3: LDOS of the (a) Si (111), (b) 4H-SiC (0001) and (c) c-BN (001) thin films calculated from the NEPs, and the surface and bulk contributions to phonons are distinguished according to their amplitudes of vibrations of surface and bulk atoms. The selected atomic vibrations of typical bulk and topological surface state-dominated phonon modes for (d, e) Si (111), (f, g) 4H-SiC (0001) and (h, i) c-BN (001) are plotted, respectively. Red squares represent for bulk modes, and black triangle for topological surface state-dominated modes.
• Figure 4: (a-c) Phonon group velocities, (d-f) lifetimes and (g-i) WPSs of the Si (111), 4H-SiC (0001) and c-BN (001) thin films with the thickness of approximately 3 nm calculated from the BTE method and NEPs, respectively. The bulk and surface modes are marked separately.
• Figure 5: The thickness-dependent lattice thermal conductivities of (a) Si (111) a-type, (b) 4H-SiC (0001) and (c) c-BN (001) thin films calculated from the BTE and HNEMD methods, and the absolute and relative contributions to lattice thermal conductivity of topological surface state-dominated phonons from the BTE are also extracted. Here, Topo. represents topological surface state-dominated mode.